docs: def com_google_fonts_check_family_equal_glyph_names(ttFonts):
    """Fonts have equal glyph names?"""
    fonts = list(ttFonts)
  
    all_glyphnames = set()
    for ttFont in fonts:
      all_glyphnames |= set(ttFont["glyf"].glyphs.keys())
  
    missing = {}
    available = {}
    for glyphname in all_glyphnames:
      missing[glyphname] = []
      available[glyphname] = []
  
    failed = False
    for ttFont in fonts:
      fontname = ttFont.reader.file.name
      these_ones = set(ttFont["glyf"].glyphs.keys())
      for glyphname in all_glyphnames:
        if glyphname not in these_ones:
          failed = True
          missing[glyphname].append(fontname)
        else:
          available[glyphname].append(fontname)
  
    for gn in missing.keys():
      if missing[gn]:
        available_styles = [style(k) for k in available[gn]]
        missing_styles = [style(k) for k in missing[gn]]
        if None not in available_styles + missing_styles:
            # if possible, use stylenames in the log messages.
            avail = ', '.join(available_styles)
            miss = ', '.join(missing_styles)
        else:
            # otherwise, print filenames:
            avail = ', '.join(available[gn])
            miss = ', '.join(missing[gn])
  
        yield FAIL, (f"Glyphname '{gn}' is defined on {avail}"
                     f" but is missing on {miss}.")
  
    if not failed:
      yield PASS, "All font files have identical glyph names."